This application discloses a valve assembly for regulating the viscosity of hydraulic fluid entering an integrated drive generator. Integrated drive generators (IDG) are used for generating electrical power on airframes. An IDG functions to produce alternating current at a specific frequency when driven by a variable speed shaft in turn driven by a main propulsion engine. The IDG is a single unit that includes a constant speed drive transmission that converts the variable speed shaft of the power main propulsion engine to a constant speed output that drives the generator. The constant speed drive transmission includes elements that require pressurized oil during the generation of electricity. These elements include a hydraulic pump and motor to provide differential cooling and lubrication for the main generator.
Proper operation of the IDG and the various component parts depends on a stable oil temperature. An increase or decrease in the temperature will change the viscosity of the oil such that the IDG no longer will operate optimally. Typically, hydraulic oil utilized in the IDG is routed through a Fuel Oil cooler that transfers heat from the oil to the fuel used to power the main propulsion engine. This method of cooling the oil is effective. However, the oil temperature and thereby the viscosity of the oil does not remain at a stable temperature which affects the efficient operation of the IDG.
For these reasons there is needed a device or assembly capable of regulating the temperature and thereby the viscosity of the hydraulic oil within an optimal range to ensure the efficient operation of the IDG.
The subject invention is a viscosity regulating valve for regulating the viscosity of a hydraulic fluid. The valve includes a housing defining a bore having first and second inlets to supply hydraulic fluid. The hydraulic fluid entering the bore through the first inlet is at a first viscosity and the hydraulic fluid entering the bore through the second inlet is at a second viscosity. As appreciated, viscosity is related to the temperature of the hydraulic fluid and therefore the viscosity of the hydraulic fluid entering through the first inlet is different than the hydraulic fluid entering through the second inlet. A spool valve having at least one land slides within the bore to proportionally block the flow of hydraulic fluid into the bore through the first and second inlets. The hydraulic fluid of differing viscosity and temperatures is mixed within the valve and exits the valve through an outlet at a third viscosity and temperature. The spool valve cooperates with the bore to form an orifice that restricts the flow of hydraulic fluid through the bore and thereby create a force to move the spool valve to proportionally block the flow of hydraulic fluid through the first and second inlets based on the value of the third viscosity and temperature.
The regulating valve of the subject invention provides a simple, precise, compact and cost effective means to regulate the viscosity and temperature of hydraulic fluid.